1. Field of the Invention
This invention relates to a depth stop for a drill, and more particularly to a depth stop device which attaches to a drill used in drilling holes in aircraft parts which insures a precise countersink of these holes.
2. Description of the Prior Art
In most traditional manufacturing processes, manipulation and processing of products are typically accomplished manually by workers. In the case of modern airplane manufacturing, this manual manipulation and processing frequently includes manually drilling a multitude of holes through titanium and the like. The accuracy of these holes can be highly dependent upon the skill of the worker. It is also necessary, in many applications, to prepare these holes with countersunk sections to enable a fastener to lie generally flush with the surface of the material. Especially in the assembly of aircraft parts, such as wings, numerous holes are required to be drilled. These drilled holes must be precisely countersunk. If they are too deep, for example, structural integrity becomes compromised and cost of producing the parts soar. The fasteners must fit flush to the material surface, and when an improperly drilled hole, meaning that the countersink is too deep, for example, occurs, a significant problem is created, which results in penalties for the manufacturer. Simply stated, a drill which included a device to insure a precise countersink to holes drilled in aircraft parts requiring a countersink, that did not depend on any particular skill of the operator of the drill would be most desirable. To this end, the prior art has produced depth stop embodiments which limit the depth within the work piece that the drill bit can travel. For illustration, a typical such device can be seen in U.S. Pat. No. 6,514,018 issued to Martinez et al. This device shows an axially oriented tightening screw which engages a sleeve. The sleeve ultimately guides the drill bit to the desired depth within the work piece, being held in place relative to the moving drill bit by the tightening screw. This particular depth stop embodiment has inherent disadvantages which are magnified when the depth of a countersunk hole, for example, must be extremely precise and repeatable. In the first place, in the manual tools suchs as drills, it is desirable that the tool be as light in weight as possible, and, of course this would also include any device attached to the drill such as a depth stop. The sleeve, therefore, that would sense the work piece and limit drilling depth is preferably has a relatively thin wall. In the common arrangement, as the above mentioned patent is an example, the sleeve would be held in place with a screw. The screw is tightened by the operator of the drill once the proper depth of the hole to be drilled is determined. The problems that can occur include deflection of the sleeve due to the force of the screw on the sleeve especially if the screw is “overtightened” by the operator. Deflection of the sleeve which controls the depth of the drilled hole will ultimately result in a lack of precision in the depth stop device. As the precision requirements increase, the deflection issue further comes to the forefront, with the ideal being no deflection of the sleeve while it is held in place and controlling the depth of the drilled hole. Even a slight misalignment of the sleeve can lead to improper countersunk holes in an aircraft part which can result in defective assembly. Over time, even with the most careful and skilled drill operators, the depth stop device shown in the above mentioned United States patent will result in manufacturing problems due to deflection of the sleeve. These problems will occur sooner rather than later as the necessary degree of precision in countersink holes increases in a particular application.
The present invention provides a solution to the problems outlined above in the prior art, by presenting a depth stop device which allows the drill to produce repeatable, precise countersunk holes in aircraft parts without relying on an unusual degree of skill by the drill operator.